1. Field of the Invention
The present invention generally relates to the separation and disposal of an undesired heavier fluid, such as water, from a desired lighter fluid, such as oil and gas, below ground surface in a production well and, more particularly, is concerned with a dual annulus production tool which facilitates the employment of a patented below production disposal (BPD) tool in wells where there is a risk of well casing corrosion from "sour" gas flowing therein above the production zone.
2. Description of the Prior Art
Oil and/or gas production wells generally produce two types of fluids, one being a desired lighter fluid, such as oil and/or gas, and another being an undesired heavier fluid, such as water or the like. Co-produced undesired fluids must be separated and properly disposed of. Traditionally, undesired fluids have been pumped to the surface along with desired fluids and then separated from the desired fluids and transported to another location where they are pumped down a separate well into a subterranean disposal formation. This "surface" approach is inappropriate for many production wells not only because it is very costly, but also because it raises the potential for adverse environmental impacts due to the possibility of an inadvertent escape of undesired fluids during transport and disposal.
Alternatively, undesired fluids can be separated from desired fluids in the production well below ground and then pumped into a disposal formation without ever being brought to the surface. This "in-situ" approach eliminates the need to transport the undesired fluids to a separate disposal well, thereby reducing the disposal costs and environmental risks associated with disposal of undesired fluids. The in-situ approach, however, requires the availability of an appropriate disposal formation. A below production disposal (BPD) tool, disclosed in U.S. Pat. No. 5,425,416 to Hammeke et al. and assigned to the assignee of the present invention, was developed to provide injection of undesired fluids into a disposal formation located below the production zone. An above production disposal (APB) tool assembly, disclosed in U.S. Pat. No. 5,579,838 to Michael and assigned to the assignee of the present invention, was developed to provide injection of undesired fluids into a disposal formation located above the production zone.
There are some wells that have candidate disposal formation zones located below the production formation zone where the patented BPD tool could be used but for the risk that "sour" gas found in these wells may corrode the casing of the well at points above the production zone, resulting in leakage that may adversely affect ground water. Environmental regulations now require that the casings of these wells be protected on the inside by loading the casing annulus with a head of non-corrosive fluid. Such regulation, while protecting the well casing, effectively prevents oil and/or gas from being removed from the well through the same casing annulus as has occurred heretofore when the patented BPD tool is utilized. Thus, a need remains for a solution to this problem in order to facilitate the use of the BPD tool in these wells for disposing undesired fluids in a lower disposal zone.